1. Field of the Invention
The invention relates to a signal preprocessing device for preprocessing output signals of structure-borne noise sensors, and to the use of the signal preprocessing device in electronic motor vehicle safety systems.
2. Description of the Related Art
It is known to use acceleration sensors within a vehicle occupant protection system for motor vehicles. Such acceleration sensors are, for example, distributed in a vehicle as what are known as assistance sensors in order to permit rapid and precise sensing of an impact or of an accident. However, this results, inter alia, in the disadvantages of a relatively large amount of costly cabling work, and in additional costs for the additional sensors. Furthermore, a large amount of cabling work also entails a certain risk in terms of failure, which can be reduced in a safety-critical environment, which a motor vehicle constitutes, by, for example, introducing redundancies.
For this reason, in order to detect an accident, use is alternately is made of structure-borne sound sensors which do not need to be arranged so close to the outer skin of the vehicle since structure-borne sound waves in the vehicle propagate much more quickly than oscillations which are generated by changes in acceleration.
Document WO 2005/036108 proposes a motor vehicle sensor of the generic type for sensing an acceleration and structure-borne sound (structure-borne sound sensor) which is used, for example, as a crash sensor. Two such sensors are arranged essentially centrally in the motor vehicle, each with different orientations. These structure-borne sound sensors (also referred to herein as noise sensors) are coupled to the vehicle chassis. Furthermore, connected downstream of these structure-borne sound sensors is a local signal processing unit which has a filter for processing signals and for selectively sensing the acceleration and the structure-borne sound. This processing unit transmits its output signals to a central control unit for evaluation. The output signals of the structure-borne sound sensors in an arrangement of this type have relatively broadband frequency spectrums and have, in particular, radio frequency signal components. The evaluation of these signals is relatively complex since, in the context of digitization of the signals, they can be sampled with more than twice the upper limiting frequency of their respectively band-limited spectrum (Shannon's sampling theorem) in order to avoid aliasing effects. This makes it necessary to use high-power and therefore relatively costly analog/digital converters in the central processing unit and is also disadvantageous in so far as a signal which is sampled at a relatively high frequency causes a relatively large amount of data in the course of digitization. This is particularly disadvantageous since the transmission channel between the sensors and the central processing unit is frequently implemented by means of a simple serial interface which does not have sufficient channel capacity under certain circumstances. In addition, the computing unit of the central processor unit which normally has to carry out a large number of processes is heavily loaded and possibly overloaded by the relatively large amounts of data.
An object of the invention is to propose a signal preprocessing device and a method for preprocessing structure-borne sound sensor signals which facilitate the use of broadband structure-borne sound sensors and/or reduces the requirements of the data interface to at least one central electronic control unit and/or reduces the amount of data to be processed by the central processing unit.